Degreasing



NOV. 12, 1935. A 1 s/NAGIE i 2,020,335

DEGREASING Filed May 5, 1933 Patented Nov.'12, `1935 PATENT OFFICE 2.020,335 DEGREASING Joseph Savage, Weston Point, Runcorn, England,

assignor to Imperial Chemical Industries Limited, a corporation of Great Britain Application May 5, i933. serial No. 669,610 In Great Britain May 6, 1932 This invention relates to an improved method and apparatus for degreasing by means of volatile solvents such as trichlorethylene.

A large number of methods and types of apparatus have been proposed for the removal of the atmosphere in additionto cooling and condensing the solvent. 'Ihis condensed water then becomes associated with thev solvent and thus comes into contact with the metalI parts of the apparatus and with the material being treated. This increases the tendency of the metals to corrode and is particularly objectionable in the degreasing of metal goods such as iron -or steel.

According to the invention I warm, to a lpredetermined extent, the cooling water vwhich is used and thereby maintain the cooling `and condensing surfaces at a temperature above the dew point of the atmosphere in which the operation is carried out, but substantially below the condensing temperature of the solvent. As a further feature of the invention, the solvent vapours are rst brought into contact with the said cooling surfaces and then uncondensed vapours are 85 brought into contact with still cooler surfaces.

AThe condensate from these last surfaces, which may be a mixture of solvent and water, is collected separately from that of the solvent vapour obtained from the flrst cooling surfaces. Complete condensation is thus effected while at the same time the main bulk of condensate remains uncontaminated by water.

In the degreasing of metal goods by means of volatile solvents, the process may be carried out in the vapour phase or in the liquid phase, that is the goods may be exposed to the vapour of a volatile solvent or may be washed by a hot or cold liquid solvent. Combinations of these various methods of working may also be made. The

present invention is ofcourse only applicable to processes involving vapour phase degreasing or treatment of the goods with heated liquid solvent.

In most forms -of apparatus for carrying out these processes the cooling Asurfaces consist of.

pipes through which a supply of cold water flows. In such cases I maintain the desired temperature of the cooling surface by slightly warming the inlet water before admitting to the cooling pipes. 'I'his may be done in many ways, for example by passing the water through a small l electrical heater or gas heater, either of which may be conveniently controlled by a thermostatic device. This method is applicable when vapour phase degreasing is used alone or when vapour phase degreasing follows a treatment with cold 1Q liquid solvent.

In an alternative method, in processes and apparatus using a degreasing bath of solvent liquor at a raised temperature and with cooling coils arranged above the surface, I pass the cooling water l5 through coils arranged in such a heated bath prior to its passage through said cooling coils. In this case the number of coils immersed in the liquid and the velocity of the cooling water are adjusted so that the desired temperature of the 20 cooling surfaces is obtained. This method may also be applied when the process is a combination of vapour phase and liquid phase degreasing using the liquid at an elevated temperature.

An apparatus adapted for carrying out the 25 process, referred to in the preceding paragraph, is illustrated in thev accompanying drawing, in which Figure l shows an elevation and Figure 2 a plan of the apparatus. Referring to Figure l, the apparatus comprises an outer casing I in- 30 side which are located the degreasing chambers 2 and 3 adapted to hold a body of liquid, and separated by the wall 4. Chamber 2 is used for degreasing in the liquid phase and 3 for degreasing inI the vapour phase. Both chambers are 35 opento the vapour space l2 in the upper portion of the casing l. The wall 4 is preferably `constructed in the fo'rm of a double wall so as to possess an insulating value retarding the transference of heat between the chambers 2 and 40 3. This enables the temperature of the chamber 2 to be more easily controlled if it is desired to 'work below the boiling point of the solvent used. Y

Heating means are provided for each chamber: 45 in the present case vthe gas burners 5 and 6 are used for this purpose although suitably arranged steam coils or electrical heating devices may be used` instead. Waste gases from the burners pass to the Outlets 1, 'l by way of the space 8 50 left between the container l and the degreasing chambers 2 and 3. This space, in addition to providing a path for the waste gases, also acts as an insulating jacket for the degreasing chambers and thus obviates excessive loss of heat by 66 radiation. In the base of the degreasing chambers thermostatic devices 9, 9, are provided-for the control of the supply of heat to the degreasing liquid. 'I'hese devices control the supply of gas to the burners 5 and 6 and prevent overheating which may occur, for example, when the volatile solvent has become highly charged with dissolved oils. This control is of greater importance in the chamber 3 since, as will be explained below, a supply of boiling solvent is maintained in the base of the chamber to supply the vapour for the vapour phase degreasing. In chamber 2 the thermostat may, if desired, be used to control the temperature at some selected point below the boiling-point of the solvent.

Cleaning doors II) and drain cocks II are fitted to the base of each degreasing chamber. In the lower portion of each of-the degreasing chambers perforated plates I3 are fitted. 'I'hese plates serve to carry the goods being treated and must be so arranged as to permit the total immersion of the goods in the solvent liquid or vapour, and also in the case of the chamber 3, to prevent contact of the goods with liquid solvent in the base of the chamber.

A set of coils I4 is arranged in the upper portion of the chamber 2. The coils are placed close to the walls of the chamber in order not to obstruct the passage into and out of the chamber of goods being treated. A suitable connection I5 to the main 2|, and provided with a valve 23 is arranged for the supply of water to the coils and an outlet pipe I6 connecting through the pipes 25 and 26 to the condensing coils I9, is provided. I also find that it is advantageous to fit a shield Il for the protection of the coils I4 against damage that might be caused by introducing or withdrawing the goods.

Towards its upper end the dividing wall 4 is provided with a small overflow outlet I8 leading from the chamber 2 to chamber 3 to enable excess liquid in 2 to pass into 3 at a relatively slow rate. This overflow is placed slightly higher than the coils I4 but at such a distance from the top of the wall 4 as to avoid a flow of liquid over the top of the wall into chamber 3 when goods are introduced into the normal volumel of liquid in chamber 2.

In the upper portion of the casing I at any convenient height above the wall 4, condensing coils I9 carried by the supports 20 are arranged round the walls. The supply of Water to these coils is from the coils I4 as previously stated and also from the main 2l through the pipe 22, tted with a valve 24, and pipes 25 and 26. At any convenient point after the junction of the pipes I6 and 22 a pocket 21 carrying a thermometer is provided for the observance of the temperature of the water entering the condensing coils. 'I'he outlet 28 for the water from the condensing coils leads to waste. Below the condensing coils, around the walls of the casing and adapted to collect the condensate flowing from the lcoils and the walls of the casing, is arranged a gutter or channel 29. Condensed solvent collected bythe gutter is delivered to the two-way cock 30 whence it flows by way of pipe 3I back to the chamber 2 or by way of 32 to a receptacle not shown, for clean condensed solvent.

A suitable cover (not shown) may be pr'ovided for the apparatus to prevent the loss of solvent ly evaporation when the apparatus is not in use.

Prior to the commencement of the degreasing operation, chamber 2 is charged with the liquid grease solvent, e. g. trichlorethylene, until it commences to flow through the overflow I8. Solvent is also introduced into the chamber 3, but in this case the volume must be adjusted so that its surface is below the perforated plate I3 even 5 when it is in a state of ebullition. It will be obvious that this is a necessary precaution if the eflicient degreasing of goods resting on the plate I3 is to lbe obtained, since after. the apparatus has been in use for some time the solvent becomes l0 charged with dissolved oils and if allowed to contact with the goods will leave a deposit or film of oil thereon which may not be removed while the goods are being raised through the vapour prior to removal from the apparatus. 15

After charging the apparatus with solvent the temperature of the chamber 2 is raised to the desired gure by means of the gas burner 5 and the solvent in 3 is heated to boiling to provide for the vapour phase degreasing. At the same time 20 the condensing coils I9 are put into operation. The temperature of these coils is adjusted as required by the invention by suitably proportioning the feed of water through the coils I4 to the feed coming directly from the main, the valves 23 and 25 24 being provided for this purpose. It would of course be possible to maintain the water at the required temperature by passing the whole supply through the coils I4 at a suitable rate. Reference to the atmospheric temperature and humidity will indicate the minimum temperature of the coils I9 for any particular condition.

In the degreasing of metal goods .in the apparatus described, they are preferably immersed first in the chamber 2 in order to remove the 85 bulk of the oil impurities. Agitation at this stage is also desirable in order that any solid impurities such as swarf or dust, which may be adhering to the goods, may be removed by the mechanical washing action of the liquid. After 4o this exposure of the liquid, the goods are transferred to the chamber 3 for removal of the residual film of oily matter which is effected by the condensation thereon of the solvent. It will, of course, be obvious that when working in this 45 manner the liquid phase degreasing must be carried out at a temperature sufficiently below that at which the solvent boils, in order that the goods may condense an appreciable amount of solvent when exposed to the vapour.

Reference has previously been made to the desired temperature in the liquid phase degreasing chamber 2. When working with trichlorethylene I have found this to be about 20-30 C. below the boiling point of the solvent. I have 55 also found that once such a temperature has been attained it is automatically maintained in this neighbourhood by the condensate from the coils I9 without the necessity of heating by means of the burner 5.

Wherever the words dew point are used herein they refer to the maximum condensation temperature of the water vapor in the atmosphere with which the cooling surfaces are in contact.

I claim:

1. An apparatus for degreasing materials comprising a vessel for receiving the materials to be degreased, said vessel being adapted to contain a volume of degreasing solvent vapor; a condenser comprising a conduit for cooling :duid 70 located in the upper portion of said vessel; and a heater arranged to heat said cooling fluid prior to its admission to said condenser.

2. An apparatus for degreasing materials comprising a vessel for receiving the materials to be 75 degreased. --said vessel being adapted to contain a volume oi' degreasing solvent vapor; a condenser comprising a conduit for cooling Huid-located in the upper portion of said vessel; and a heater arranged to heat said cooling fluid to a temperai ture above the dew point of the atmosphere prior to its admission to said condenser.

3. An apparatus for degreasing materials comprising a vessel for receiving the materialsto be degreased. said vessel being adapted to be partially filled with a volatile liquid degreasing solvent; means ior heating said liquid solvent; a condenser comprising a conduit for cooling uid located in the upperportion of said vessel; and a heater arranged to heat said cooling uid prior to its admission to said condenser, said lheater comprising a conduit arranged within the body of said liquid solvent.

4. An apparatus for degreasing materials comprising a vessel for receiving materials to be degreased, said vessel being adapted to be partially lfilled with a. volatile liquid degreasing solvent;

means for heating said liquidv solvent; a condenser comprising a conduit for cooling fluid located in the upper portion of said vessel; and a heater arranged to heat said cooling :Huid to a temperature above the dew point of the atmosphere prior to its admission to said condenser, said heater comprising a conduit arranged within the body ofsaid liquid solvent.

JOSEPH SAVAGE. 

